linux-kernel - Re: [PATCH v2 11/21] x86/virt/seamldr: Allocate and populate a module update request

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Message-ID: <aS6POwWg4C7sPwsn@intel.com>
Date: Tue, 2 Dec 2025 15:03:23 +0800
From: Chao Gao <chao.gao@...el.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
CC: <linux-coco@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
	<x86@...nel.org>, <reinette.chatre@...el.com>, <ira.weiny@...el.com>,
	<kai.huang@...el.com>, <dan.j.williams@...el.com>,
	<yilun.xu@...ux.intel.com>, <sagis@...gle.com>, <vannapurve@...gle.com>,
	<paulmck@...nel.org>, <nik.borisov@...e.com>, Farrah Chen
	<farrah.chen@...el.com>, "Kirill A. Shutemov" <kas@...nel.org>, Dave Hansen
	<dave.hansen@...ux.intel.com>, Thomas Gleixner <tglx@...utronix.de>, "Ingo
 Molnar" <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin"
	<hpa@...or.com>
Subject: Re: [PATCH v2 11/21] x86/virt/seamldr: Allocate and populate a
 module update request

On Thu, Nov 27, 2025 at 04:30:41PM +0800, Binbin Wu wrote:
>
>
>On 10/1/2025 10:52 AM, Chao Gao wrote:
>[...]
>> +
>> +/* Allocate and populate a seamldr_params */
>> +static struct seamldr_params *alloc_seamldr_params(const void *module, int module_size,
>> +						   const void *sig, int sig_size)
>> +{
>> +	struct seamldr_params *params;
>> +	const u8 *ptr;
>> +	int i;
>> +
>> +	BUILD_BUG_ON(sizeof(struct seamldr_params) != SZ_4K);
>> +	if (module_size > SEAMLDR_MAX_NR_MODULE_4KB_PAGES * SZ_4K)
>> +		return ERR_PTR(-EINVAL);
>> +
>> +	if (!IS_ALIGNED(module_size, SZ_4K) || !IS_ALIGNED(sig_size, SZ_4K) ||
>> +	    !IS_ALIGNED((unsigned long)module, SZ_4K) ||
>> +	    !IS_ALIGNED((unsigned long)sig, SZ_4K))
>> +		return ERR_PTR(-EINVAL);
>> +
>> +	/* seamldr_params accepts one 4KB-page for sigstruct */
>> +	if (sig_size != SZ_4K)
>According to the link [2] you provided above, it seems that the layout of
>tdx_blob as following:
>tdx_blob
>|- u16      version
>|- u16      checksum
>|- u32      offset_of_module  --------------------------------------|
>|- u8       signature[8]  |
>|- u32      len                                     8KB + (N * 4KB) |
>|- u32      resv1 |
>|- u64      resv2[509]  |
>|- u8       data[]  |
>            |- _u64 sigstruct[256]   //2KB sigstruct  |
>            |- _u64 reserved2[256]  |
>            |- _u64 reserved3[N*512] //4KB aligned, optional, N >=0  |
>            |- _u8  module[]  //<-----------------------------|
>
>If N is not 0 for reserved3, then the sig_size passed will not be 4KB.

The "reserved3[N*512]" is there for future extension.

The current P-SEAMLDR ABI only supports one 4KB page, so if a blob's sig_size
is larger, the kernel has to reject it. The P-SEAMLDR ABI should be extended
first, and then we can add kernel support accordingly.

>
>
>> +		return ERR_PTR(-EINVAL);
>> +
>> +	params = (struct seamldr_params *)get_zeroed_page(GFP_KERNEL);
>> +	if (!params)
>> +		return ERR_PTR(-ENOMEM);
>> +
>> +	params->scenario = SEAMLDR_SCENARIO_UPDATE;
>> +	params->sigstruct_pa = (vmalloc_to_pfn(sig) << PAGE_SHIFT) +
>> +			       ((unsigned long)sig & ~PAGE_MASK);
>
>Since sig is 4KB aligned, is ((unsigned long)sig & ~PAGE_MASK) needed?

This is done intentionally. Otherwise, we would need to assume PAGE_SIZE is
4KB. Although this is true for x86, just in case it changes in the future and
subtly breaks this code, I use SZ_4K and apply PAGE_MASK here.

<snip>

>> +static struct seamldr_params *init_seamldr_params(const u8 *data, u32 size)
>> +{
>> +	const struct tdx_blob *blob = (const void *)data;
>> +	int module_size, sig_size;
>> +	const void *sig, *module;
>> +
>> +	if (blob->version != 0x100) {
>> +		pr_err("unsupported blob version: %u\n", blob->version);
>
>Based on the link [2], 0x100 stands for version 1.0, Using hexadecimal seems
>more readable.

Makes sense. Will do.